Thanks for the advice,
Yesterday, I have removed the top and back panels to inspect the washer. Everything seems OK. The main pulley isn't warped and the bearing on the back shell also looks good.
Strangely, the washer didn't vibrate violently as it use to. I'm suspecting that the drum may have made contact with the back panel.
BUT, there's still an issue. On the normal cycle, the washer won't spin. I though the washer was acting that way because of the vibration but it isn't the case. After the rinse cycle it starts to spin to stays at about 100-300 rpm for about a minute or so. Then the cycle completes. Afterward, I have selected the drain/spin cycle and it did spin properly (high rpm for about 3-5 minutes).
So it doesn't sound like it's a mechanical problem. What would be the cause of a washer that won't spin correctly only when the normal cycle is selected?